Various rubber tire components have been proposed for various purposes such as, for example, tire treads for use during winter driving for snow and ice conditions as well as rubber reinforced cord plies and belts.
Rubber tire treads intended for winter driving have sometimes been fitted with metal studs to enhance their traction on icy roads. However, the use of such metal studded tires has sometimes been somewhat restricted at least in part due to potential damage to roads over which they travel.
Rubber tire treads which have a cellular foam rubber, particularly rubber containing closed cells, for their running surfaces have also been proposed for winter traction. For example, see U.S. Pat. Nos. 5,176,765, 5,351,734, 5,788,786, 6,021,831 and 6,497,261.
Alternatively, some tire treads have been proposed for winter driving conditions which are composed of elastomers which have low glass transition temperatures (Tg's), namely Tg's below −30° C. (e.g. from about −30° C. to about −105° C.). Such low Tg elastomers may inhibit or at least reduce excessive hardening of the tread rubber composition at the very low ambient operating temperatures with a view toward providing softer rubber treads to promote better traction and handling for snow and ice conditions.
Silica reinforcement of selected elastomers has been suggested for tire treads intended for winter conditions. For example, see U.S. Pat. No. 5,616,639.
Other winter tread rubber compositions designed to improve tire traction on ice include the aforesaid use of low Tg rubbers, as well as use of low temperature plasticizers designed to provide a general reduction of the tread composition's hardness at low temperatures.
Historically, substantial amounts of silica reinforcement in combination with a silica coupling agent has sometimes been used as a primary or predominant reinforcement for various rubber blends in rubber tire treads. For example, see U.S. Pat. Nos. 4,519,430; 5,066,721; 5,227,425 and 5,616,639. Use of various coupling agents to achieve reinforcement of the rubber composition by coupling the silica to the elastomer(s) is well known. However, it is considered herein that such silica/coupler reinforcement is often not, by itself, entirely sufficient for suitable enhanced ice traction for a tire tread.
Tire treads which are silica reinforced with coupling agent which also contain cellulose fibers, wood fibers and/or ceramic hollow spheres have also been suggested for tires to be driven under winter ice conditions. For example, see U.S. Pat. No. 5,967,211.
However, it is considered herein that it remains desired to provide tire treads with enhanced traction for driving under winter conditions as well as for seasonal conditions other than winter conditions.
In the description of this invention, the terms “rubber” and “elastomer” where used herein unless otherwise prescribed, are used interchangeably. The terms rubber “composition” or “compound” where used herein, unless otherwise prescribed, generally refers to a composition in which one or several rubbers are blended or mixed with various ingredients or materials. A term “compounding ingredient” where used herein unless otherwise prescribed, generally refers to ingredients used to prepare rubber compositions, or compounds. Such terms are well known to those having skill in the rubber mixing and compounding art.
The term “corncob granules” is used herein to refer to corncob granules which are obtained from the woody ring surrounding the central core, or pith, of the corncob. The corncob granules are manufactured by drying the woody ring portion, or fraction, of the corncob followed by grinding to produce the granules which are air cleaned and separated into various sizes by mesh screening. Such corncob granules are manufactured by The Andersons, Inc. and sold as Grit-O' cobs® corncob granules, for example as 60 Grit-O' cobs®. For further corncob granule discussion, see “Use of Fine-R-Cobs as a Filler For Plastics”, by D. B. Vanderhooven and J. G. Moore, reprinted from the Internal Wire and Cable Symposium 1982.
The term “phr”, where used herein and according to conventional practice, refers to parts by weight of respective material per 100 parts by weight of rubber.
The Tg of a rubber or rubber compound, where used herein unless otherwise prescribed, refers to its glass transition temperature which can be conventionally determined, for example, by differential scanning calorimeter at a heating rate of 10° C. per minute. It is understood that such Tg determination is well known to those having skill in such art.
The term “butyl type rubber” is used herein in a general sense of a rubbery isobutylene/conjugated diene copolymer or halogenated isobutylene/conjugated diene copolymer which is typically comprised of from about 1 to about 5 weight percent units derived from said diene, wherein the diene is typically isoprene and is typically simply referred to as a butyl rubber. The halogen of said halogenated rubber is typically bromine or chlorine as a brominated butyl rubber or chlorinated butyl rubber. Butyl rubber and halogenated butyl rubbers are well known to those having skill in such art.